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commandlinefu.com is the place to record those command-line gems that you return to again and again.

Delete that bloated snippets file you've been using and share your personal repository with the world.
That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and
voted up or down.

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Follow the Tweets.

Every new command is wrapped in a tweet and posted
to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning,
there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.

The output of "echo $PATH" is hard to read, this is much easier. The parentheses ensure that the change to the input field separator (IFS) only happens the the sub shell and not affecting the current shell.

I am new to linux, and I was trying to figure out why I could not sudo with my username in Fedora 10. This command, when run as root, will add a line to the sudoers file allowing the loginname supplied to sudo. The above line will require a password when you sudo, if you wish to sudo without password, use:

echo 'loginname ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers

instead. you have to run this command as su, and this is just an easier way of using visudo, just adds it right from the terminal.

One of the many things it regularily checks for is world writeable files.

If any are found, it writes the list to /var/log/security/writable.today.

"wc -l" simply counts the number of lines in the file.

This number should be low.

Browse through /var/log/security/writable.today and consider if any of those files *need* to be world-writeable (and if not, modify the permissions. eg: "chmod o-w $file").

A large number of world-writeable files may indicate that umask is not correctly set in /etc/profile (or ${HOME}/.bash_profile) but could also indicate poor security configuration or even malicious activity.

This command sequence allows simple setup of (gasp!) password-less SSH logins. Be careful, as if you already have an SSH keypair in your ~/.ssh directory on the local machine, there is a possibility ssh-keygen may overwrite them. ssh-copy-id copies the public key to the remote host and appends it to the remote account's ~/.ssh/authorized_keys file. When trying ssh, if you used no passphrase for your key, the remote shell appears soon after invoking ssh user@host.

This invokes tar on the remote machine and pipes the resulting tarfile over the network using ssh and is saved on the local machine. This is useful for making a one-off backup of a directory tree with zero storage overhead on the source. Variations on this include using compression on the source by using 'tar cfvp' or compression at the destination via

A simple but effective replacement for ps aux. I used to waste my time running ps over and over; top is the way to go. It also allows complex sorting options. Press q to exit "nicely" (Ctrl + C is always an option, of course). Note that the list updates each second, resorting in the process; if you're trying to grab a specific PID, you might be better off with ps.

htop

Alternatively, htop is available, though it may not come pre-installed. htop is slightly more interactive than top and includes color coding, visuals, and a nice interface for selecting and then killing processes. (Thanks to bwoodacre for this great tool.)

You're running a script, command, whatever.. You don't expect it to take long, now 5pm has rolled around and you're ready to go home... Wait, it's still running... You forgot to nohup it before running it... Suspend it, send it to the background, then disown it... The ouput wont go anywhere, but at least the command will still run...